What are vapor cones? A vapor cone is made when an aircraft is flying at transonic speed. Air moving over the aircraft goes fast at some parts of it, and the air goes slower at the other places. This generates lift, which helps the aircraft fly. When the aircraft is at transonic speed, the air above the aircraft is accelerating at supersonic speeds. So at the back of the aircraft there's a sonic boom, and then that sonic boom slows the air back to its normal speed. That causes the air pressure and temperature to be lowered suddenly. If air temperature is low, then that same air cannot hold much water vapor hence, making a vapor cone. Bonus Click here for a nice surprise! Glossary transonic-below but near the speed of sound supersonic-above the speed of sound